Communication path delay measurements play an important role in the analysis, design and monitoring of networks. However, the clock skews (or frequency differences) between the clocks at the end points of the path can render the delay measurements inaccurate. To obtain more accurate delay measurements, the clock skews have to be accurately estimated and removed from (or compensated for) in the measurements.
End-to-end communication path delay traces are often used to analyze network performance. The measured path delays can be used to improve the design of networks, optimize the placement and use of network resources, monitor network loading and availability, optimize traffic routing and control mechanisms, detect network faults and traffic flow anomalies, etc. Delay traces are typically obtained by monitoring packet delays or by active probing. In either case, the difference between the arrival time of a packet (measured according to the destination clock), and its corresponding departure time from the source (indicated by a timestamp added by the source and conveyed by the packet), is considered to be the delay experienced by that packet.
If the source and destination clocks are perfectly synchronized, then the measured delay is the true delay between the two end points. However, in real systems, two clocks are rarely perfectly synchronized. The clocks can run at different speeds (i.e., have different frequencies). This difference in speed or frequency is called the clock skew. Given that the clocks at the end systems are not perfectly synchronized and run at different speeds, the delay measurements can be quite inaccurate. To obtain more accurate delay measurements, the clock skews have to be accurately estimated and removed from (or compensated for) in the measurements [1][2][3][4][5][6]. Network protocols such as the Network Time Protocol (NTP) and IEEE 1588 Precision Time Protocol (PTP) can be used for clock synchronization as well as perform network delay measurements.